Just like you, I do not know exactly how a matchline is represented in the Revit database.
You can discover that for yourself by following the standard steps to research how to solve a Revit API programming task; in short, create the object of interest manually in the user interface and use RevitLookup and other tools to explore what changed in the database:
- https://thebuildingcoder.typepad.com/blog/2017/01/virtues-of-reproduction-research-mep-settings-ontology.html#3
- https://thebuildingcoder.typepad.com/blog/2013/11/intimate-revit-database-exploration-with-the-python-shell.html
Once you know what database elements represents the matchline, you can explore its properties, relationships and geometry, and things will become much clearer.
Looking forward to hearing what you find out.
Thank you!
Best regards,
Jeremy